Plan well and you won't need to find water to filter. I don't occasionally, but have always managed, even in the west. Been offered water by passing motorist, bummed off RVers, and used faucets at private homes. Good planning is far better, and as noted by prathmann, finding water to filter can be nearly impossible.

Even in populated areas of the US, best to keep 3 liters topped off, especially if you're wild camping. Out west, 5 liters minimum, especially in the summer. 5 plus a gallon in some really isolated stretches. I hate having worry about water mess up the joy of carefree pedaling.